I'm trying to send my purchase order using the realted field ::Email_suppliers.

It opens Outlook and has the attachment etc but does not have the supplier's address in the address bar.

Just some sanity checks: Is a supplier specified for this particular PO? Does the supplier in question have an e-mail entered?

(Just checking …it's frustrating to hunt for logic errors only to find that in fact data was missing).

Is the context correct at the time the script reads the field? What do you see when you place the related e-mail address field on the PO layout where the script executes?

And last but not least, I suggest using the Debugger and the Data Viewer.